1. Field of the Invention
The present invention relates to an ink jet print device with exchangeable printheads for reproduction of single-color and/or multicolor characters and/or graphic patterns, which ink print device is movable back and forth in print line direction along a recording substrate.
2. Brief Description of the Background of the Invention Including Prior Art
A printhead construction is known from the German printed patent document DE-OS 2,843,064 for use in connection with ink jet printing devices, where a plurality of exit nozzles disposed at a high density are provided. Individual ink droplets are ejected from the ejection exit nozzles and are thrown against a recording substrate. The ejection of the droplets in such a so-called "drop on demand printhead" is performed under the influence of thermoelectric converter elements. The thermoelectric converter elements are arranged in the shape of heating registers on a substrate. The thermoelectric converter elements are individually controllable and the thermoelectric converters are coordinated to individual ink channels. An ink jet vapor bubble is generated in the respective ink jet channel upon control of a heating resistor, where the ink vapor bubble leads to an ejection of an individual ink droplet. This method, which has become known under the concept of bubble jet technology, allows the construction of an ink jet writing device having a high resolution capacity, wherein the write head can be constructed with many closely spaced nozzle openings.
Such ink printheads exhibit a limited lifetime based on wear manifestations and aging processes. Causes for possible operating disturbances, which can lead to failures of the ink jet printers, are among others also a drying up of ink or a superficial drying of the writing liquid, marked changes of the viscosity of the writing liquid or soiling or, respectively, cloggings of the nozzle region by extrinsic particles such as, for example, paper dust. A destruction of the concave ink meniscus at the nozzle end can also lead to disturbances and, in an extreme case, to an operational failure in case of ink jet printers operating under negative pressure.
In order to assure an undisturbed operation of such ink jet writing devices, it is conventional to construct the printheads for approximately a lifetime corresponding to the useful lifetime of the printer or to accept an expensive overdimensioning. A necessary exchange of printheads employed for a lifetime can usually only be performed by skilled service personnel but not by the personnel operating the writing device.
A writing apparatus is known from the German printed patent document DE-3,342,895 with an ink writing mechanism exhibiting an exchangeable writing head for the generation of different character fonts. In order to assure a safe handling during the exchange of the write head, in particular in order to avoid a contamination of the ejection nozzles and an entrance of air into the interior of the printhead, there is furnished a locking device on a slider. The locking device can be automatically coupled with a control lever disposed in the frame upon return of the slider into the rest position, where the printhead is disposed in a protected position outside of the writing region. The locking device is pivotably supported at two end positions for the decoupling and for the coupling of the printhead and of the ink container. An easy exchange of the printhead is made possible by this construction and the print operation can be continued disturbance-free at any time after such exchange.
The European printed patent document EP-0,255,867-A2 shows an ink print apparatus, which is suitable both for multicolor as well as single-color printing based on exchangeable ink jet printheads. The ink jet printhead is exchangeably mounted on the carriage based on a support structure, wherein a first kind of ink printhead is coordinated to the single-color ink printing, and wherein a second kind of ink printhead is coordinated to the multicolor ink printing. A coding matrix is disposed between the control circuit proper of the print device and the exchangeable ink jet printhead. Upon a change from one ink printhead of the one kind to an ink printhead of the second kind (multicolor), the coding matrix automatically connects the respective connections for the control arrangement. This coding matrix can be provided in this case as plug connection, wherein the individual plug contacts are connected with plug-in switches or jacks, wherein the plug-in switches or jacks close the corresponding connections upon insertion of the ink jet printhead into the support structure. In addition there is provided a sensing device. The sensing device captures the kind of ink jet printhead employed and, dependent on the kind of ink printhead employed, switches a coding matrix connecting the nozzles with the control circuit and/or actuates a display device.
An exchangeable ink jet print device formed as a cassette is known from the IBM Technical Disclosure Bulletin, Volume 17, No. 9, February, 1975, pages 2622-2623, which includes one single ink jet printhead for the printing of single color characters or patterns. The ink jet print device is in this case disposed stationary in an ink jet print apparatus, while the recording substrate to be imprinted is moved past the nozzle opening of the ink jet printhead, and wherein thereby the ink jet droplets are applied. The cassette can be connected to the lower part of the print device via a screw connection. The electrical connection and contacting or, respectively, the ink supply is thereby performed via pins and separate ink supply tubes.
The U.S. Pat. No. 4,703,332 shows an ink jet printhead, which is disposed such as to move along a recording substrate in the print apparatus, and where the ink jet printhead exhibits one single nozzle, and where the ink jet printhead operates with an electrically conductable ink. Two electrodes are furnished for the ejection of ink. One of the electrodes is in contact with ink and a counter electrode is disposed in proximity of the nozzle. An electrical voltage pulse is applied to the electrode. The electrical voltage pulse effects an evaporation of ink in proximity of the nozzle opening and, associated therewith, an ejection of an ink droplet from the nozzle. Several such ink jet printheads are furnished for the representation of color recordings and each individual head of the plurality of such ink jet printheads is disposed inside a cassette casing containing the ink jet fluid. The ink supplies have to be moved in this case together with the print apparatus carriage. A metallic blade and an electrically conductive lever serve for the contacting of the two electrodes of each head with a control device supplying the pulses, where the metallic blade and an electrically conductive lever engage into recesses of the cassette casing.
A further possibility for furnishing exchangeable ink jet printheads in a simple manner comprises to arrange the container for the ink supply immediately at the ink jet printhead, such that when such a head is exchanged, the complete unit comprising ink jet printhead and ink supply is replaced, as disclosed in European printed patent document EP-0,125,742-B1. This is associated with the advantage that upon exchange of such a throw-away unit no fluid mechanical connections have to be coupled, however, the time intervals between the individual exchange procedures are short based on the relatively small supply of writing liquid in the simultaneously moved reservoir.